Glass-to-metal seal and process for making the seal



y 17, 1951 J. B. LEUZARDER ETAL 2,563,061

GLASS-TO-METAL SEAL AND PROCESS FOR MAKING THE SEAL Filed Dec. 17, 1947 INVENTOR5 Patented July 17, 1951 GLASS-TO-METAL SEAL AND PROCESS FOR MAKING THE SEAL John B. Leuzarder, Verona, Jens J. Aakjer, R-

selle, and William John Knochel, East Orange, N. 3., assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application December 1'7, 1947, Serial No. 792,268

6 Claims.

This invention relates to seal and lead-in construction and method of manufacture, and specifically refers to the means and method of sealing lead-in wires or posts through glass enclosures in electrical apparatus such as lamps, electronic I tubes and the like.

'sults in poor adhesion of the glass bead to the lead-in wire and excessive oxidation results in formation of leakage paths through the oxide when the envelope is evacuated.

The present invention proposes uniform oxidation of the lead-in wires under controlled conditions and sealing of the bead thereto without material change in the amount of oxide at the seal.

The invention further contemplates stem assembly in a single heating operation for the glassto-metal and glass-to-glass seals.

A further object of the invention is to both rc- 1glluce time and steps in fabrication of stem assemies.

Other objects of the invention will appear to those skilled in the art to which it appertains as the description thereof proceeds both by direct recitation thereof and by implication from the context.

Referring to the accompanying drawing in which like numerals of reference indicate similar parts throughout the several views;

c Figure l is an elevation of an electrical device wherein our invention is employed in fabrication of the stem assembly shown therein;

Figure 2 is an elevation, partially broken away, showing the completed stem assembly;

Figure 3 is a sectional View of the stem assembly in processof fabrication and showing portions of the apparatus utilized in carrying out the method involved; and

Figure i is a cross-section on line IV-IV of Figure 3.

In the specific embodiment of the invention illustrated in said drawing, the selected electrical device in which the invention is incorporated is an electronic tube of the diode type known specifically as a Rectigon or rectifier, and comprises a vacuum-tight envelope 8, usually of glass, having a screw-base H at one end making electrical connection with lead-in wires l2, I3 within the tube which carry therebetween a cathode M which is also Within the envelope. At the other end of the envelope is a stem assembly [5 which provides a flare [6 the rim of which is integrally sealed to the wall of the envelope at a neck end i! thereof. The stem assembly includes a leadin wire or post it longitudinally therethrough with a tear-drop glass seal thereon at the inner end of the flare. A press-seal may be employed, however, in place of a tear-drop seal if desired. Within the envelope, the lead-in wire carries an electrode, such as anode IS, in proper spaced relation to above-mentioned cathode I4.

The present invention inheres more particularly in the stem assembly and its method of manufacture. In carrying out the invention, a quantity of lead-in wires are first oxidized according to a fixed schedule so as to have an oxide coating thereon of predetermined character and thickness. Usually the lead-in wires l8 are tungsten and according to this invention are oxidized in groups of one to five hundred at a time. A baking period of five to ten minute's in air at a temperature of approximately 600 C., obtaining an oxide coating from .00003 to .00099 inch, has proved to be the desired range, with preference given to seven and a half minutes baking for a coating of substantially .00006 inch. The lead-in wires I8 are of adequate dimension, say about inches in diameter, to be sufiiciently rigid that they are adapted to serve each as a supporting post for the anode shown herein or for other uses to which adapted.

Fabrication of the stem assembly utilizes power-driven apparatus, of which the portion herein shown includes a rotating sealing head 29 the axis of rotation of which is vertical. Said sealing head 29 is operatively mounted-upon and constantly rotated by a usual construction of sealing machine well known in the prior art. The sealing head 28 is hollow and receives a socket member 2i therein to rotate therewith, said socket member having a coaxial socket 22 therein of proper diameter and depth to receive and support the lead-in wire or post It coaxial to the axis of rotation and with predetermined protrusion of the post from the upper. end of the said member.

The seal of the glass portion of the stem is accomplished upon the oxidized post immediately above and where protruding from the member.

Above the socket member 2| as a part of said sealing machine, there is provided a flare support 23 recessed coaxial to the axis of the said member and in spaced relation thereabove, which enablesaglass stem-tube 24 to be hung therein by itsflare I6 coaxially around the protruding part of the post 18, but with the lower end of the said tube out of contact from said member thereby providing a gap 25 between the lower end of the glass tube and the upper-end of the socket member. The flare support 23 rotates at the same speed as and with the rotating sealing head 20 and socket member 2|.

Further above the sealing head 20 and above the said flare support 23, also aspartof said sealing machine, are provided means for gripping the upper end portion of the post, said means being herein indicated as gripping 'fingers 26 diametrically opposed to each other on opposite sides of the post, These gripping fingers 26 likewise revolve about the common axis of rotation of the sealing head 20,. fiare sup- .port 23, and post l8, at the same speedasand with the rotating sealing'head 20.

. In the assembly of the work in the machine,

the post I8 is dropped into the socket 22 of the socket member 2| and its upper end is gripped by said gripping fingers 26 for rotating said post; the flaredglass stem-tube 24 is hung in the recess of the flare support 23;'and ashort sleeve.

of glass herein designated a floating bead 21, whichslidably fits upon the protruding portion of the post, is slid down thatpost until the lower end of said sleeve of glass or floatingbeadzl "rests upon the upper end of the socket member ,2l.

This bead 21, because of frictional contact, will rotate with the post 18 and socket member 2 I. The glass preferred for said glass sleeve .or' floating bead 21 is one of appropriate character to have approximately the same coefficient of expansion as the metalcomprising post 18.

.The glass of flared tube 24 may be of the same characteristic as that of the sleeve, or may be somewhat different in its coeflicientof expansion to provide a graded seal from the post l8 to en--,.

velope' l0.

With the work pieces assembled in the machine as above described, they. aresimultaneously rotated and flames 28 from burners 29 are played upon the glass tube 24 at the lowerend thereof below the flare support 23 .and immediately-above the socket member 2|. Part of the flame and heat enters gap 25 and-as a=consequence the glass of both the tube 24' and-sleeve or bead 21 softens and shrinks'inwardly initially :atithe lower extremity of each. Continuedrapplication of the flame results in .the'tube24 sealing with sleeve or bead 21 and the bead'withwthe I post l8 as a simultaneous or continuing'operation of thermal sealing. If 'so desired,.and particularly when sealing rmore than one lead-in eral sleeves r beads 21, thereby forming a flat press at the end of the stem.

It is now appropriate and important to point out that an effective seal between glass and metal in general requires surface oxidation of the metal. In particular, to obtain a vacuum tight-seal-between glass'and tungsten, the'surface of the tungsten: must be coated with an oxide. The best oxide for tungsten-to-glass seal tungsten oxide. However, it has been further,

4 determined that excessive oxidation creates a condition of a crust of oxide interposed between the tungsten and the glass, and that such a crust contains shrinkage cracks or crevices .through .which ,air may-seep-.longitudinally of the sealland'thus void the desired vacuum within the envelope. On the other hand, an oxide coating of minute thickness seems to intermingle with the glass for improving the bond, with the glass actually in engagement with the tungsten, and therefore no crust and no crevices are present. The above described oxidation schedule has been found to give the requisite oxide coating, neither too thin nor too thick.

, reventing entry .of additional air, (3) from the fact the glass seals first next thelower end of the bead, thereby preventing. entry-of oxygen from below, and (4) from the fact rising heat and gases in the slight space between post and bead prevent influx ofoxygenat theupper end iofstherbead. Consequently .the bead not. only constitutes a sealing .medium'with the tungsten, but during the sealing thereof to the. tungsten rconstitutes.aprotector against further oxidation.of the. tungsten .within. rthe sealing region.

The seal thus. effectedis one wherein a predetermined amount of the tungsten oxide-is presented to andabsorbed by the glass juxtaposed to .the tungsten bead, so that the. mingling of oxide with the glassis confined to practically only thesurface layer of the glass next the tungsten thereby strengthening the bond. between thev glass and tungsten without spreading .intoand weakening the body of glass by dispersion therein beyond the surface thickness thereof. Penetration of the oxide into the glass, orwhat-is herein termed surface thickness of the glass, appears to beapproximately double the thickness of the oxide coating on the metal at the time the seal .is effectedthat is .to say up to about .0002 inch.

Weclaim:

1. Aiglass-to-metal sealcomprising a metallic part and a glasspart thermally bonded, the juxtaposedsurface'ofthe glass to the metal having a predetermined quantitativel limitedmetal oxide therein confined .to immediate vicinity of bonded contact with the metal of said metallic the glass to the metal and providing a surface of intermingled oxide and glass toward and in partsubstantiallyto the exclusion of oxide film between the glassand metal.

. 2. .A glass-.to-metal seal comprising a tungsten part and a glass part thermally bonded, the juxtaposed surface of the glass to the tungsten having-a predetermined quantitatively limited metal oxide therein. confined to immediate vicinity of the glass to the tungsten and providing a surface of intermingled metal oxide and glass toward and in bonded contact with the tungsten of said tungsten part substantially to the exclusion of metaloxide film between the glass and. tungsten parts.

3. A glass-to-metal seal comprising a tungsten part and a glass part thermally bonded. the juxtaposed surface of the glass to the tungsten having a tungsten oxide therein quantitatively limited to an amount of tungsten oxide obtainable from a film thickness on the metal part less than .00009 of an inch and confined to the immediate vicinity of the glass to the tungsten and providing a surface of intermingled tungsten oxide and glass toward and in direct bonded contact with the tungsten of said tungsten part substantially to the exclusion of oxide film between said tungsten part and glass part.

a. A method of eifecting a glass-to-metal seal comprising oxidizing a metal part with an oxide coating substantially between .00003 and .00009 inch in thickness, protecting the area to be sealed of the oxidized part and preventing further oxidation thereat, and thermally sealing the glass at the protected part of said oxidized metal area and obtaining dispersion of substantially all of the oxide coating at said area from the metal into the glass and confined to surface penetration in the glass of said oxide and obtaining bonded contact directly with the metal of the metal part by the glass containing the metal oxide.

5. A method of effecting a glass-to-metal seal comprising oxidizing a tungsten lead-in post at a predetermined heat of approximately 600 C. for a predetermined time in the approximate range of five to ten minutes and obtaining a coating of tungsten oxide within the range of substantially .00003 to .00009 inch in thickness on said post, protecting the portion of the length of said post from further oxidation at the area Where sealing is to be effected, and thermally sealing glass to said post at said protected area and obtaining dispersion of substantially all of the tungsten oxide coating at said area from said tungsten post into the glass and confined to 6 surface penetration in the glass of said oxide and obtaining bonded contact directly with the tunesten of the tungsten lead-in post by the glass containing the tungsten oxide.

6. A method of effecting glass-to-metal seal of a lead-in post in a stem assembly, comprising supporting a lead-in post in a socket member, applying a glass sleeve on said post with an end of said sleeve against said member, locating a stem tube around said sleeve with the end of said tube towardsaidmemberspacedtherefromiorproviding a gap therebetween for entry of flame and heat to the end margin of said sleeve, and directing a flame to said sleeve and tube next said gap and into said gap for progressively sealing the sleeve to the post beginning at the member-engaging end of the sleeve and simultaneously sealing the tube to said sleeve.

JOHN B. LEUZARDER.

JENS J. AAKJER.

WILLIAM JOHN KNOCI-IEL.

REFERENCES CITED The following references are of record in the OTHER REFERENCES Procedures in Experimental Physics, (pg. 24), by John Strong et al., pub. by Prentice-Hall Inc., N. Y., 1944. 

